If you’re importing dates from Excel into R with the gdata package, you might get some funny numbers instead of the dates you’re expecting. These numbers represent the number of days from January 1, 1904 (or 1900) depending on what version of Excel the dates were entered in.
This StackOverflow question helped me get numbers like 40693 looking more like dates. So something like
worked for me. I don’t really know why I had to use 1899-12-30 for the origin – I thought should use 1900-01-01, but that was off by a couple days. 1899-12-30 gave me the right dates, so I won’t argue. I will, however, be double checking the other dates for weirdness.